I am a huge fan oh W231, but there are just certain limitations where we try to drive it too far. Jeep - I do the same as you. W231 is my primary pistol "stockpile" powder, and it is at least as good as average, if not ideal, in many loads and calibers. I use it in the following:

380 ACP (practice & full-power loads)
9mmP (practice loads)
38 Spl (practice & full-power loads)
357 Mag (practice loads)
10mm (practice loads)
44 Russian (practice loads)
44 Spl (practice & full-power loads)
44 Mag (practice loads)
45 ACP (practice, target, & full-power loads)

In particular answer to your question, Jeep, load 4.0grs W231 w/ 158gr SWCs in either 38 or 357 and you'll have great results. I find this to be VERY accurate in most guns, and its at the top end of power for the 38 without having to worry about alloy-frame guns. Its powerful enough to let you feel you're shooting something, but light enough to let most people focus on accuracy.

I've tried W231 in the higher ranges which are "certified safe" in the older loading manuals. My opinion is that they've eliminated these loads NOT out of safety, nor out of laziness - just publishing the cowboy loads... I believe they experienced, or got enough questioning querries, or both, about the change in combustion characteristics with W231 at "magnum levels."

I've found in 357 & 44 Magnums that as the pressure approaches or exceeds 25-30k (even though still in the "safe zone"), W231 is no longer a pleasant, accurate, nor ideal powder. I've noted substantially increased recoil and muzzle blast, lower accuracy, and a different smell to the consumed powder under these circumstances.

I've noticed similar but less-pronounced issue in 10mm. Even at high pressures in the 9mm, I don't notice the problem at all. I've theorized from this experience that case volume, or more-accurately: unused space inside the case, when combined with higher pressure for this powder is the causal factor.

The bottom line is that W231 CAN be safely loaded for a medium-power 357 load, but I think you'll be dissatisfied with the results.